Defrost arrangement for air conditioning apparatus



Feb. 7, 1961 w. J. MQCARTY 2,970,816

DEFROST ARRANGEMENT FOR AIR CONDITIONING APPARATUS Filed Aug. 51, 1959INVENTOR WILLIAM J' McCARTY 42.

BY W

H is ATTORNEY Unite DEFROST ARRANGEMENT FOR AIR CONDI- TIONING APPARATUSFiled Aug. 31, 1959, Ser. No. 837,141 3 Claims. (Cl. 257-278) Thepresent invention relates to air conditioning apparatus of the type usedduring cold weather to supply heat to an enclosure and more particularlyto an arrangement for quickly defrosting the evaporator of suchapparatus.

In air conditioning units of the type which are used for supplying heatto an enclosure during the winter months, the evaporator of the unit isexposed to the outdoor air and, if the outdoor temperature becomes toocold, the evaporator rapidly accumulates a coating or layer of frost.The frost layer operates as a barrier to heat transfer and, as thethickness of the layer of frost increases, the efficiency of the airconditioning unit for supplying heat to the enclosure is markedlyreduced.

. The frost layer on the evaporator usually builds up at an acceleratedrate as the outdoor temperature becomes lower and lower. This has theeffect of reducing the heat output of the unit when it is most needed.

Most units now on the market provide supplementary heating in the formof resistance heaters to augment the 7 output of the air conditioningunit during these low outdoor temperatures. In addition, some unitsprovide defrosting means for melting the layer of frost on theevaporator whenever it begins to affect the efiiciency of the unit sothat heat can be supplied by the refrigeration system even during thelower outdoor temperatures. Defrosting has been carried out in the pastby use of resistance heaters disposed adjacent the evaporator or bypassing hot gas from the refrigeration system directly through theevaporator for melting the frost layer. The latter type of arrangementis normally considered to be the most desirable since it does notrequire the additional resistance heating means or the additionalelectrical wiring and connections in the wet atmosphere of theevaporator. However, hot gas defrost arrangements are usually slower inoperation and, in those systems which reverse the refrigerant flowtherethrough for purposes of defrost, there is the added disadvantagethat the heat exchanger being used to supply heat to the enclosurebecomes cold and reduces the heat supply to the enclosure. The presentinvention is an improvement over both of the abovementioned types ofdefrost arrangements and eliminates the disadvantages of thesearrangements.

It is an object of the present invention to provide, in an airconditioner of the type adapted to heat an enclosure, an improveddefrost arrangement which uses hot gas to melt the frost on theevaporator and which is so arranged as to take advantage of theresistance heat already provided in the air conditioner to enhance thedefrosting operation.

It is another object of the present invention to provide an improveddefrost arrangement which utilizes heat as well as hot gas to melt thefrost while requiring no electrical connections in the moist atmosphereof the evaporator compartment.

A more specific object of the present invention is to provide animproved defrost arrangement utilizing the flow of warm refrigerantthrough the evaporator coils to melt the'frost and to provide thearrangement with additional heat input from the auxiliary heater toassure an adequate supply of vaporous refrigerant flow through thesytsem during the defrost period.

Further objects and advantages of the invention will become apparent asthe following description proceeds, and the features of novelty whichcharacterize the invention will be pointed out with particularly in theclaims annexed to and forming a part of this specification.

In accordance with the present invention, there is provided an airconditioning unit having the usual refrigeration system including anevaporator, a condenser, and a compressor connected in refrigerant flowrelationship with a refrigerant expansion means between the evaporatorand the condenser for producing a pressure drop in the system betweenthese two members. The unit is provided with fans or air moving meanswhich, during theheating season, are adapted to circulate separatestreams of air from the inside and from the outdoors over thecondenserand the evaporator respectively. The unit is also provided with aresistance heater for supplying additional heat to the enclosurewhenever the refrigeration system is unable to supply sufiicient heat tomaintain the enclosure at the desired temperature. To quickly defrostthe evaporator of the unit during the heating season after an excessivebuildup of frost thereon, there is provided a refrigerant bypass passagewhich is opened by a frost sensing means to shunt the refrigerant fromthe condenser around the expansion means directly into the evaporator.In order to maintain a sufficietly high suction pressure during thedefrost operation so that an adequate supply of vaporous refrigerant ispumped through the system and to add heat to the vaporous gas to enhancethe defrosting operation, the above-mentioned supplementary heater ispositioned so that it heats the condenser and, thereby, also heats therefrigerant flowing through the condenser. The frost sensing means forinitiating the defrosting operation also energizes the supplmenetaryheater to supply heat to the condenser even though the temperatureconditions of the enclosure may be such as not to require the additionalresistance heat.

For a better understanding of the invention references may be had to theaccompanying drawings in which:

Fig. 1 is a plan view of an air conditioner unit incorporating thepresent invention; and

Fig. 2 is a line diagram illustrating the components of the airconditioner with an arrangement for initiating the defrost operation andfor simultaneously energizing the supplementary heater.

Referring now to the drawing, in Fig. 1 there is shown an airconditioner of the self-contained type including a casing 2 adapted tobe mounted in an aperture or window in the outer wall of an enclosurewith one side of the casing facing the enclosure 3 and the other side ofthe casing exposed to the outdoors 4. The casing is divided by a barrier6 into two separate compartments hereinafter designated the condensercompartment 7 and the evaporator compartment 8. Within the casing is arefrigeration system including a condenser 9, an evaporator 11, and acompressor 12 connected in refrigerant flow relationship. The evaporator11 is positioned in the evaporator compartment 8 while the condenser 9and the compressor 12 are both mounted in the condenser compartment 7.Suitable expansion means such as the capillary 10 or an expansion valveare provided between the condenser 9 and the evaporator 11 for producingthe required pressure drop in the refrigerant system between these twomembers. An accumulator 15 is provided in the system between theevaporator 11 and the compressor 12 for collecting liquid refrigerantwhich, under certain conditions of operation, overflows from theevaporator. The accumulator 15 stores liquid refrigerant and preventspatented Feb. 7, 1961' it" from flowing'directly into the compressor.During operation of the illustrated air conditioner, the evaporatoralways removes heat from the air within the evaporator compartment 8while the condenser 9 discharges heat or is cooled by'the air within thecondenser compartment 7.

The evaporator compartment is divided into air inlet and outlet sections13 and 14 respectively by a fan shroud l6 and a fan 17 which alsocirculates air through theevaporator compartment. A closure panel 18,which may be moved to either the enclosure or outdoor facing sides (asindicated by the dotted lines in Fig. l) of the evaporator compartment,makes it possible to circulate either outdoor or enclosure air throughthe evaporator compartment to be cooled by the evaporator. Similarly,the condenser compartment is divided by the shroud 19 and a fan 21 intocondenser compartment inlet and outlet sections 22 and 23. A closurepanel 24, similar to panel 18 in the evaporator compartment, is arrangedto direct air into the inlet section 22 either from the outdoors or fromthe enclosure merely by moving the panel from one side of the condensercompartment to the other.

With the closure panels 18 and 24 positioned as shown in Fig. l, the airconditioner is adapted to heat the enclosure 3. More specifically, airis circulated through the condenser compartment 7 from the enclosurewhere his heated by the condenser and discharged back into the enclosureas indicated by the arrows in Fig. 1. Outdoor air is drawn into theevaporator compartment inlet section 13 where it encounters theevaporator 11 and gives up heat to the evaporator and is then dischargedto the outdoors again through the outlet section E4. The refrigerantflowing through the system delivers to the condenser 9 the heat removedfrom the outdoor air by the evaporator 11. In order to provideadditional heat for the enclosure whenever the refrigeration system ofthe unit is not capable of maintaining the desired temperature withinthe enclosure, there is provided an auxiliary or supplementary heater 25in the form of a resistance heater. The heater 25 is positioned in thecondenser compartment and heats the air circulated therethrough.Normally, the operation of the heater 215 is made automatic according tothe temperature of air within the enclosure. The heater 2.5 is usuallyenergized by a thermostat (seen only in Fig. 2) whenever the roomtemperature drops a certain number of degrees below that set by theoccupant. That is, if the thermostat was set at 75 F. and the actualroom temperature fell to 70 F., it would be an indication that the heatload of the room was more than could be met by the refrigeration systemalone, and the supplementary heater 25 would then be energized to addadditional heat.

The outdoor air in passing over the evaporator 11 is cooled and depositsa certain amount of moisture on the coils and evaporator surfaces. Undercertain conditions which normally occur when the outdoor temperature isabove a certain temperature, such as 42 F., the evaporator operates at atemperature above the freezing point of water. Under these conditions,the water deposited on the evaporator by the outdoor air drops from theevaporator into a suitable collection tray or sump 26 in the bottom orlower portions of the evaporator compartment. This water is removed fromthe unit through the drain 27 and suitable drain conduits (not shown)which lead to the outdoors or to any other suitable drain area. However,whenever the outdoor temperature drops too low, such as below thetemperature of 42 F, the operating parameters of the refrigerationsystem cause the evaporator temperature to drop below 32 F. or below thefreezing point of water. Under these latter conditions of operation,there is a build-up of frost on the evaporator 11. This frost barrieracts as an insulation and prevents effective heat transfer between theevaporator coils and the air within the evaporator compartment, thus,greatly decreasing the amount of heat removed from this 4. 7 air which,in turn, decreases the heat output at the condenser.

As will now be explained, the present invention deals with anarrangement for defrosting the evaporator whenever the frost build upthereon reaches a predetermined amount. Referring to Fig. 1, there isshown a refrigerant bypass passage 28 which -is connected between thecondenser 9 and the evaporator 11 which is designed to shunt refrigerantfromthe condenser around the capillary 10 directly to the evaporator.During normal operation of the system the bypass passage 1% is closed,but means are provided in the form of a defrost control 29 and a valve31 for opening the passage whenever the frost build up on the evaporatorbecomes too great. In the air conditioner of Fig. 1,. the defrostcontrol 29 is meant to schematically illustrate a pressure actuatedswitch which is energized whenever the pressure drop across theevaporator is a predetermined amount. Thus, as the frost buildup on theevaporator increases and the'space for the flow of air through theevaporator becomes more and more restricted, the pressure drop acrossthe evaporator gives an indication of the frost build upon theevaporator. whenever the pressure drop across the evaporator is such asto indicate an undesirable amount of frost build up on the evaporator.

It will be understood that the defrost sensing control device 29 is notlimited, merely, to a pressure'drop sens ing device or switch and maycomprise any of the well known frost sensing devices readily availableon the market, such as the temperature sensing bulb 29b and bellowsactuator 29a shown in Fig. 2. These are well known in the art and adetailed explanation of the various types available or the operationthereof isnot believed necessary except to say that the device must becapable of sensing conditions resulting from a predetermined frost buildup on the evaporator and must be capable of actuating a valve eitherdirectly or indirectly, such as shown in Figs. 1 and 2, through theenergization of an electrical switch which, in turn, initiates movementof a valve.

In Fig. 1, whenever there is a predetermined pressure drop across theevaporator, resulting from the restric-' tion caused by the frostbuild-up on the evaporator, the defrost control 29 energizes thesolenoid 31a of the valve 31 which then moves to the open position. Inthis manner warm liquid refrigerant or vaporous refrigerant is passed orshunted directly into the evaporator for heating and, thereby,defrosting the evaporator. In the process of warming the evaporator,much of the refrigerant in the evaporator is condensed and collects inthe accumulator 15 which is made large enough to store all of the liquidrefrigerant in the system to prevent slugging of the compressor withliquid during the defrost period. Because the compressor is no longerworking against a. head pressure, except for the small pressure droppresent in the tubing of the system, the vaporous refrigerant is nolonger compressed to any great extent as it passes through thecompressor and its temperature is greatly reduced. In fact, if theoutdoor temperature is very low most of the refrigerant within thesystem condenses out and collects in the accumulator 15 thereby reducingthe pressure of the system. This leaves very little gaseous refrigerantto be pumped by the compressor as well as greatly reducing thetemperature of vaporous refrigerant that is pumped. This condition,which will hereinafter be referred to as running out of gas, greatlyincreases the length of time required to defrost the evaporator.

In order to prevent the system from running out of gas" during thedefrost cycle and to provide additional heat for quickly defrosting theevaporator, the auxiliary or supplementary heater 25 is so positionedwithin the condenser compartment 7 that it also. supplies heat to thecondenser 9; Thus, as may be seen. in Fig. l, the.

heater 25 is disposedclosely adjacent the. condenser and The control 29initiates the defrost cycle during defrosting of the evaporator, thesupplementary heater 25 is energized to heat the refrigerant flowingthrough the condenser 9. During the defrost cycle, operation of the fans17 and 21 is normally discontinued so that a great amount of the heatfrom the heater 25 is carried by radiation through all portions of thecondenser. This, of course, raises the temperature of the vaporousrefrigerant immediately supplied to the evaporator and, of course,hastens the melting of the frost layer. The addition of heat at thecondenser 9 also warms the gas flowing through the system and maintainsa suflicient quantity of refrigerant at a high enough temperature toprevent it from condensing out and causing the system to run out of gas.Thus, an adequate quantity of vaporous refrigerant is continuouslypumped through the system for carrying the heat added at the compressorto the evaporator.

The use of a means, such as described above, for quickly defrosting theevaporator 11 makes it possible to operate the refrigeration system ofthe air conditioner to supply heat to the enclosure at times when theoutdoor temperature is well below 32 F., or below the freezing point ofwater. This means that the condensate sump 26 in the evaporatorcompartment 8 will be exposed to tem peratures cold enough to freezewater. In order to prevent the drain 27 of the sump 26 from becomingfrozen shut and to assure drainage of water from the sump duringdefrosting of the evaporator, the bypass conduit 28 is provided with aplurality of turns 32 which circulate in contact with the sump 26 andwhich heat the sump during the defrosting operation. The turns 32utilize the heat added by the auxiliary heater 25 to raise thetemperature of the sump 26 and drain 27 above the freezing point ofwater making it possible to drain the water melting from the evaporator.

During operation of the unit on the heat cycle, there are times when theevaporator requires defrosting under operating circumstances when thesupplementary heater is not normally energized because the temperaturewithin the enclosure is being adequately maintained by the refrigerationsystem. That is, at times, the refrigeration system is capable ofsupplying all of the heat necessary to maintain comfort conditionswithin the room so that there is no need for additional resistance heat,but the frost build-up on the evaporator is such as to necessitatedefrosting thereof in order to permit a continued efficient operation ofthe system and a continuous supply of heat. When this occurs, it isdesirable to energize the auxiliary heater just for the purpose ofobtaining quick defrost. An arrangement for accomplishing this purposeis shown in Fig. 2 which illustrates the components of the air con-'ditioner in schematic form. Power is connected to the unit through thepower lines 33 and 34 and the main switch 35. A thermostat 36, of anywell known type now on the market, is provided for controlling theoperation of the compressor or the refrigeration system through theswitch 37. The thermostat also controls the energization of theresistance heater 25 through the switch 37 according to the needs of theenclosure. The heater 25 is shown wrapped around a portion of thecondenser 9 to indicate that it is positioned closely adjacent thecondenser for supplying heat thereto during the defrost operation. Aswas previously pointed out, frost condi' tions on the evaporator 11 aresensed by a control device which, in the modification illustrated inFig. 2,, is shown as a temperature sensing bulb 29b and expansionbellows 29a.

The temperature sensing bulb of the control device is shownschematically in position adjacent the last portion of the evaporatorconnected to the accumulator 15. It is this portion of the evaporatorwhich normally operates at the coldest temperature and, it is here wherethe frost build up is generally the greatest. The bulb 29b is sopositioned with respect to the evaporator coils as to sense lower andlower temperatures as the frost build upon the evaporator increases.

Thermostat 36 energizes the heater whenever switch 38 is moved to engagecontact 39. This is normally accomplished by making the switch 38movable to the dotted line position whenever the thermostat senses atemperature within the enclosure that is a predetermined number ofdegrees, such as 4, below the temperature set for the enclosure. Forexample, if the occupants of the enclosure desire a temperature of 72 F.in the enclosure and set the thermostat to maintain this temperature,the

switch 38 will move to its dotted line position across the contact 39whenever the thermostat senses a temperature of 4 below 72 F., or 68 F.At all other times the switch 38 opens or breaks the circuit throughcontact 39.

When frost conditions occur, the bulb 29b and bellows 29a operate switch30a to connect the electrical current to the solenoid 31a which in turnmoves the valve 31 into the open position. Closing of the switch 31aalso places the heater 25 into the circuit by energizing the heatercircuit 42 through the line 41. In this way the heater is alwaysenergized during the defrost cycle even though the thermostat 36 may notactually be conditioned to energize the heater 25 through the contact39. As may be seen in Fig. 2, the solenoid and heater circuit energizedby the switch 30a are connected in parallel. Furthermore, theenergization of the heater 25, during frost conditions when switch 30ais actuated to supply power to the solenoid 31a, does not depend uponthe temperature conditions sensed by the thermostat 36. Thus, theenergization of the heater 25 is controlled by either the thermostat 36or by the frost sensing control device so that the heater alwayssupplies heat to the condenser during defrost operation regardless ofthe temperature of the air within the enclosure.

By the present invention there is provided, for an air conditioneradapted to heat an enclosure, a defrost arrangement for therefrigeration system thereof which utilizes resistance heat for meltingthe frost on the evaporator but which does not require that the heaterbe positioned closely adjacent the evaporator or within the moistatmosphere of the evaporator compartment. Furthermore, the airconditioner of the present invention utilizes a single resistance heaternot only for supplying heat to the enclosure but also for the additionalpurposes of defrosting the evaporator and for melting ice within thecondensate sump.

While, in accordance with the patent statutes, there has been shown anddescribed what at present is considered to be the preferred embodimentof the invention, it will be obvious to those skilled in the art thatvarious changes and modifications may be made therein without departingfrom the invention and it is, therefore, the aim of the appended claimsto cover all such changes and modifications as fall within the truespirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In an air conditioning unit of the type adapted for heating air froman enclosure comprising a refrigeration system including a compressor, acondenser and an evaporator connected in refrigerant flow relationship,an accumulator connected in said refrigeration system between saidcompressor and said evaporator for temporarily storing liquidrefrigerant overflowing from said evaporator, a supplementary heaterarranged in close proximity to said condenser for supplying additionalheat to said enclosure under certain ambient conditions and for heatingsaid condenser, refrigerant expansion means connected in said systembetween said evaporator and said condenser, a normally closedrefrigerant bypass conduit connected between said evaporator and saidcondenser for bypassing refrigerant pumped by said compressor throughsaid condenser around said expansion means to said evaporator, meansresponsive to frost conditions on said evaporator for opening saidbypass to permit fiow of unexpanded'refrigerant liquid or hot gas fromsaid condenser for defrosting said evaporator, said means alsoenergizing said supplementary heater to heat said condenser duringdefrost periods so that refrigerant gas flowing through said condenseris heated and an'adequate quantity of vaporous refrigerant is pumped bysaid compressor through said system at a sufficiently high temperatureto assure quick defrost of said evaporator.

2. In an air conditioning unit of the type adapted for heating air froman enclosure comprising a refrigeration system including a compressor, acondenser and an evaporator connected in refrigerant flow relationship,refrigerant expansion means connected in said system between saidevaporator and said condenser, a condensate sump for collectingcondensate water from said evaporator, means for directing separatestreams of air from inside and outside said enclosure over saidcondenser and said evaporator respectively, a supplementary heatingmeans arranged in close proximity to said condenser for supplyingadditional heat to said air flowing over said condenser and forsupplying heat to said condenser, a condensate sump for collectingcondensate water from said evaporator, a normally closed refrigerantbypass conduit connected between said evaporator and said condenser forbypassing refrigerant pumped by said compressor through said condenseraround said expansion means to said evaporator, said by pass ccnduitincluding several turns thereof positioned in close proximity to saidcondensate sump for heating said condensate sump during the flow ofrefrigerant through said bypass conduit, and means responsive to thefrost condition on said evaporator for opening said bypass conduit topermit flow of unexpanded refrigerant liquid or hot gas from saidcondenser for defrosting said evaporator and said condensate sump, saidmeans also energizing said supplementary heater to supply heat to saidcondenser during defrost periods so that refrigerant gas flowing throughsaid condenser is heated and an adequate quantity of vaporousrefrigerant is pumped by said compressor through said system at asutliciently high temperature to assure quick defrost of said evaporatorand said condensate sump.

3. In an air conditioning unit of the type adapted for heating air froman enclosure comprising a refrigeration system including-a compressor, acondenser and an evaporator connectedin refrigerant flow relationship,an ac curnulator connected in said refrigeration system between saidcompressor and said evaporator for temporarily storing liquidrefrigerant overflowing from said evaporator, a supplementary heater forsupplying additional heat to said enclosure under certain ambientconditions, said supplementary heater being arranged in close -proximityto said condenser for heating said condenser, refrigerant expansionmeans connected in' said system between saidevaporator and saidcondenser, a condensate sump for collecting condensate water from saidevaporator, a normally ciosedi refrigerant bypass conduit connectedbetween said evaporator and said condenser for bypassing refrigerantpumped by said compressor through said condenser around said expansionmeans'to said evaporator, said bypass conduit including several turnsthereofpositioned in close proximity to said condensate sump forheatingtsaid condensate sump during the flow of re.- frigerantthrough-said bypass conduit, meansresponsive to frost conditions on saidevaporator foropening said bypass conduit to permit flow of unexpandedrefrigerant liquid or hot gas from said condenser for defrosting saidevaporator and said condensate sump, said means also energizing saidsupplementary heater to heat said condenser during defrost periods sothat refrigerant gas flowing through said condenseris heated and anadequate quantity of vaporous refrigerant is pumped by said compressorthrough said system at a sulficiently high temperature to assure quickdefrost of said evaporator and said condensate sump.

References fitted in the file of this patent UNITED STATES PATENTS2,635,433 Schordine Apr. 21, 1953 2,672,734 Ditzler et al Mar. 23, 1954-2,806,674 Biehn Sept. 17, 1957

